The present invention relates to devices for the fixation and/or support and/or replacement of bone structure. In particular, the present invention relates to bone treatment implant assemblies, including a bone treatment implant body and one or more spring structures, all directed to treatment, stabilization and/or replacement of bones of e.g. the spinal column or stabilization of long bones.
Specifically, this invention is directed toward failure avoidance, namely toward avoiding bone screws in surgical implant assemblies from backing out of, withdrawing from the implant assembly and/or bones to which they have been mounted, thus preventing e.g. nerve, muscle, and/or vascular damage which can be done by such withdrawn screw.
Implant assemblies of the present invention have particular application in situations where compression or settling forces, as well as torsional and flexing forces, of e.g. “fixed” vertebrae or a long bone, on a bone treatment implant assembly, cause significant stressing and potential failure of one or more elements of the bone treatment implant assembly, or unacceptable stressing or other deleterious effect on the bones being treated.
Bone fixation and bone replacement have become common approaches for treating bone-related disorders, fractures, and the like, and for fusion of vertebrae at the time such fixation is instituted. Namely, one or more bones or bone fragments may be fixed in position relative to one or more other bones or bone fragments. Generally, a bone treatment implant, e.g. a spinal plate, is the device of choice used for mechanically supporting cervical vertebral fixation. Lower in the spine, implants known as “cages” may be used to replace deteriorated natural bone structure.
A typical implant plate includes an implant body having a plurality of apertures therethrough. A plurality of fasteners, e.g. bone screws, are generally positioned into and through respective ones of the apertures of the implant to thereby attach the implant to bone, such as to two or more respective upper and lower supporting adjacent spinal vertebrae. The screws are fastened to the respective support vertebrae to thereby attach the implant body to healthy supporting bone structure in the patient. In general, such implant assemblies can be utilized, for example, for fixation of cervical, lumbar, and/or thoracic portions of the spine.
The basis of implant fixation is to use screws to solidly mount the implant body to healthy bone tissue, thus to provide support to the bone structure being treated. In addition to the application of, for example and without limitation, a spinal plate or cage, bone graft material may be combined with the vertebrae, or vertebrae elements, as an assist in permanently fusing together adjacent vertebrae or other bone material. The graft material can consist of bone graft material obtained from bones of the recipient, or bone graft material obtained from another individual.
A common problem associated with the use of such bone implants is the tendency of the bone screws to “back out” or pull away or otherwise withdraw from the natural bone or bones into which the screws are mounted. This problem of “backing out” occurs primarily as a response to the normal motions of the body skeleton as the patient goes about his or her daily activities/routine. This is a particularly important problem in that, as screws become loose and pull away or withdraw from the bone, the heads of the screws can rise above the surface of the implant and, possibly, even work their way completely out of the bone. While this condition can cause extreme discomfort for the recipient user of the implant assembly, namely the patient, any substantial withdrawal of the screws from the bone/implant can also create a number of potentially serious physiological problems if and when withdrawn portions of such screws interact with the significant amount of nervous and vascular tissues located at or near the implant site in the body.
A number of plate assembly designs and cage assembly designs have been proposed in attempts to prevent screws from pulling away from, or withdrawing from, the bone and/or to prevent the screws from backing out of, or pulling away from, or withdrawing from, the surface of the implant assembly. Such mechanisms used to stabilize the position of the implant and/or the bone screws include a cam which engages the screw, alternately a cap mounted to overlie the bone screw, alternately a bone screw having a head which bites into the side wall of the implant body aperture, alternately a cover screw whose head overlies an adjacent bone screw, alternately knives which are rotated so as to cut into healthy bone tissue after placement and securement of the implant assembly, and alternately springs which intrude into the withdrawal path of the bone screws.
All of these designs have certain limitations, including parts releasing from the implant assembly, potential for breakage of a screw, or assemblies which require particular precision and alignment in their application or implementation in order to work as intended. Additionally, loose components and accessories of spinal implant assemblies, which address the “backing-out” or withdrawal problem, can get dropped and/or misplaced during the fixation surgical procedure, prolonging and complicating the procedure which results in increased risk of harm to the patient.
Yet another common phenomenon associated with the use of such spinal implant assemblies is the tendency, of vertebrae which are being treated, to settle after the implant assembly has been installed. Such settling may add compression forces to the above-listed forces. In some embodiments of bone implants, slots may be used in the implant body to accommodate such settling, thus to limit the amount of stress imposed on the screws.
It would be desirable to provide bone treatment implant assemblies which facilitate secure bone-to-implant fixation and/or support, such as at e.g. adjacent or second adjacent vertebrae, while providing screw back-out protection structure which is securely fixed to the implant body and which enhances stabilization of the implant assembly in the living body.
It would further be desirable to provide bone treatment implant assemblies which afford substantial protection against pulling away or withdrawal of mounting screws, which pulling away or withdrawal may result from e.g. torsional movement, flexing movement, or stress and/or dynamic load sharing of the bone being treated, the protection thereby enhancing the bone rebuilding process carried on routinely by the living body.
It would be still further desirable to provide bone treatment implant assemblies comprising an implant body and a back-out prevention structure having resiliently movable spring-like members, having resilient properties, the assemblies being so mounted and positioned as to enable bone screws to move past such spring-like members, with corresponding flexing or other movement of such spring-like members, when the bone screws are being installed in a patient and which, in combination with the designs of the bone screws, prevent unintentional withdrawal of the bone screws after installation of the bone screws in the patient being treated.
It would be still further desirable to provide a spring structure, both alone and in a bone treatment implant assembly comprising a bone treatment implant body, wherein the spring structure includes resiliently movable spring-like material having resilient properties, including a spring leaf, wherein the spring structure is secured, at least in part, to the implant at the spring leaf.
It would be yet further desirable to provide a spring structure wherein the spring structure is secured, at least in part to the implant body at the spring leaf, in combination with enabling limited movement of the spring leaf relative to the implant body, and further enabling passing such limited movement from the spring leaf to the spring bands.
It would be yet further desirable to enable such limited spring movement by use of an aperture in the spring leaf, spaced from opposing ends of the leaf, and wherein a stud extends from the implant body into, optionally through, the aperture.
It would optionally be desirable to provide such limited spring movement by use of a spring leaf structure having an intermediate anchor element which is located beyond the longitudinal ends of the bands such that the bands can be fully enclosed within a channel in the implant body while the anchor element is fixedly secured to the implant body at the end of the channel.
It would be further desirable to provide bone treatment implant assemblies, such as spinal plate assemblies or spinal cages, which can be completely pre-assembled such that no assembly steps need be performed on the implant assembly, itself, as part of the surgical procedure wherein the implant assembly is being installed in a patient.
It would be still further desirable to provide bone treatment implant assemblies wherein apparatus, in such bone treatment implant assemblies, for preventing withdrawal of bone screws from the bone, after installation of the bone screws in a patient, are automatically activated, to prevent such withdrawal, as a consequence of the installation of suitably-configured such bone screws.